March 5, 2018 | IOP Science

Urban agriculture (UA) has been undergoing a global resurgence in recent decades, with cities in both advanced and emerging economies implementing programs to encourage its use (Mok et al 2013, Orsini et al 2013, Hamilton et al 2013, Vitiello and Brinkley 2013). This renewed interest has led to the exploration of the extent to which UA could be expanded, including a number of investigations that estimate the potential for UA to meet local food demand; for example, Grewal and Grewal (2012), McClintock et al (2013) and Goldstein et al (2017), suggest provision of total food demand (former) and vegetable demand (latter two), of 4.2%−17.7%, 5% and 32%, respectively. Expanding UA is expected to improve local sustainability, including benefits to social (addressing food deserts, building community cohesion, or higher intake of fresh produce) and economic (cash crop production, reduced food costs) facets of cities. The environmental aspects associated with the net direct and indirect energy implications of UA will be the primary sustainability focus area of this research.

Part of the rationale for reconsidering UA has been its potential environmental benefits, including reductions in energy demand throughout the food supply chain. As a result, UA has been included in greenhouse gas (GHG) mitigation strategies for cities (Arup and C40 Cities 2014) and broader urban sustainability agendas through multi-city agreements and partnerships, such as the UK’s Sustainable Food Cities Network and the Milan Urban Food Policy Pact, the latter of which includes 100 large cities around the world (Milan 2015, Andrews et al 2017). However, when considering the complex interplay between food production, energy requirements, and water availability (i.e. the food–energy–water nexus), the ability of UA to reduce energy demand is unclear.

This review article examines energy use in the food system, explores the opportunities that exist for high-income cities to increase the energy/resource efficiency of this overall system through UA, and proposes changes that could be made in the planning of cities to enable greater reductions in energy demand, with a focus on the United States. The scope extends beyond the frequently-assessed topic of transportation into topics such as embodied energy of production inputs (i.e. water, nutrients, heating, CO2), reduction in packaging, storage, and processing needs. This review aims to provide a point of reference for energy considerations that should be made if UA is going to provide a greater share of the global food supply.

Classifying urban agriculture

Estimating the current scale of UA is difficult and varies based on how it is defined; for example, Thebo et al (2014) estimate that there were 67 megahectares (Mha; 106 ha) of UA8globally in 2000 (5% of global arable land in that year; Food and Agriculture Organization 2010, table A4), with roughly 1/3 of the UA area being irrigated. Their quantification includes spatial data where agricultural areas and urban boundaries with populations greater than 50 000 overlap, most of which would be classified as peri-urban9 agriculture and would not capture small-scale operations such as residential gardens, vacant lots, or building-integrated production (e.g. balcony gardens, rooftop gardens). Inclusion of peri-urban agriculture would produce a substantially higher estimate of UA than the area that is currently used in these more commonly-perceived forms of UA. Looking at the scale of some of these types of UA, Taylor and Lovell (2012) examine the total area of UA in the city of Chicago using 2010 aerial photographs. They find that approximately 0.04% of Chicago’s land area of 606 km2 was being used for urban agriculture; of this, nearly half (45%) was in residential gardens, while most of the remainder was in vacant lots (27%) and community food gardens (21%). To provide a sense of scale of the opportunity to expand urban agriculture, a 2000 study of vacant land in US cities finds that those in the Midwest had an average of 12% vacant land, and a national average of 15% (Pagano and Bowman 2000)10.

As alluded to above, UA manifests itself in a number of different structures and locations within the built environment. Attempts have been made in the literature to classify UA; Mok et al (2013) identify three distinct scales of agriculture in urban systems. These are (in order of decreasing size): small commercial farms and community-supported agriculture, community gardens, and backyard gardens. All of these UA scales differ in their structure, inputs, and productivity; as a result, their net impact on life cycle energy demand, and other resource inputs, also varies. Goldstein et al (2016b) further classify UA to consider structure and inputs in a taxonomic scheme, based on the conditioning required for the growing environment (temperature, light and CO2 control) and integration within the surrounding urban system (building integrated or ground based). They claim that both features are important to UA energy regimes, with space conditioning (particularly the need for heating in cold climates) being an essential consideration, along with the potential for building integrated farms to utilize dissipative heat and CO2 to offset production inputs.

A broad classification of UA is provided in table 1, which is roughly ordered by scale and sophistication of production. It should be highlighted that while the preservation of peri-urban agriculture can be captured in assessments of UA, the focus of this review is on approaches to scaling up UA that are integrated into the built environment, rather than on maintaining existing agricultural land in the urban periphery. Hence, large scale conventional peri-urban agriculture is beyond the scope of inquiry here.

To read the rest of the study, please follow this link: http://iopscience.iop.org/article/10.1088/1748-9326/aa889b